This invention relates generally to the field of insoluble oxidation catalysts, and more specifically to novel complexes of chromium metal catalysts supported on an insoluble polymer having pendant pyridine groups. These complexes have shown themselves to be useful in catalyzing various oxidation reactions as described more fully below.
Considering one such reaction for the moment, it involves the oxidation 1,2,3,4-tetrahydronaphthalene (available commercially under the trademark Tetralin.RTM. by Du Pont de Nemours, E. I. & Co.) to 3,4-dihydro-1(2H)naphthalenone, which is commonly referred to as ".alpha.-tetralone." About 35,000 tons of .alpha.-tetralone are produced in the United States each year for use as an intermediary in the manufacture of methyl-1-naphthylcarbamate, an insecticide generically referred to as carbaryl and commercially available under the trademark Sevin.RTM., as well as in the manufacture of other agricultural chemicals and drugs. Typically, .alpha.-tetralone has been prepared by the liquid phase autoxidation of Tetralin.RTM. in the presence of a homogeneous oxidation catalyst, and possibly also a homogeneous catalyst modifier in an attempt to improve reaction selectivity to .alpha.-tetralone. The oxidation product mix normally obtained in such reactions includes .alpha.-tetralone, 1,2,3,4-tetrahydro-1-naphthol, which is commonly referred to as ".alpha.-tetralol," and .alpha.-Tetralin.RTM. hydroperoxide.
A fundamental problem with these homogeneous oxidation catalyst processes has been the relative difficulty in isolating the desired .alpha.-tetralone or other product from the reaction mix, regardless of selectivity. Not only must the undesired reaction by-products be separated from the desired product, but the homogeneous oxidation catalyst and homogeneous catalyst modifiers of the prior art must also be separated out and recovered for subsequent reuse. As a result, the isolation of desired product, such as .alpha.-tetralone, has historically required additional time-consuming distillation and other processing procedures, thereby increasing production and other costs.
Such problems exist with the Tetralin.RTM. oxidation catalyst and catalyst modifier disclosed in U.S. Pat. No. 3,404,185 issued to Thomas, et al. Thomas discloses a homogeneous Cr(III) acetate oxidation catalyst that is used in the presence of a homogeneous heterocyclic aromatic amine catalyst modifier, 5-ethyl-2-methylpyridine which is commonly referred to as MEP. The reaction product reportedly obtained is a mixture of .alpha.-tetralone and .alpha.-tetralol in approximately a 20:1 ratio, and .alpha.-Tetralin.RTM. hydroperoxide. As reported in Thomas, et al., the presence of MEP as a catalyst modifier apparently improved the selectivity of the oxidation reaction to .alpha.-tetralone due to the presence of pyridine ligands in the MEP. However, for efficient and effective operation, the catalyst and catalyst modifier must be separated from the homogeneous product mix through a series of steps as reported in Thomas, et al. And even then, full recovery and regeneration of the catalyst and modifier for reuse are in doubt.
Many other examples exist in the art of homogeneous oxidation catalysts and modifiers which have been used in the synthesis of .alpha.-tetralone, with varying degrees of success. Some of these include the following: U.S. Pat. No. 3,404,185 (Cr(III) acetate+MEP); Mizukami et al., Bull. Chem. Soc. Jpn. 1979, 52, 2689 (Cr(III) acetate+DMF); Israeli No. 41,114 (Cr oxide+2,4.6-trimethylpyridine); USSR No. 565,910 (1977) (Co(II) salts+polyurethane); Japan Kokai No. 76.101.964 (Cr(III) naphthenate+piperidine); Ger. Offen. DE No. 2,508,334 (Cr(III) naphthenate+2,4-lutidine); Japan Kokai No. 75.558.044 (aqueous CrO.sub.3 +lutidines); and U.S. Pat. No. 4,473,711 (Chromium(III)-exchanged Dowex CCR-2+MEP).
It has also been reported in U.S. Pat. No. 4,473,711 issued to Coon that .alpha.-tetralone has been prepared by the liquid phase autoxidation of Tetralin.RTM. in the presence of a Cr(III)-exchanged carboxylic acid resin such as Dowex.RTM. CCR-2 which is commercially available from Dow Chemical U.S.A. Dowex.RTM. CCR-2 is reported to be a weak acid cation exchanger containing carboxylic acid groups within an acrylic-divinylbenzene matrix. However, Coon used this heterogeneous catalyst in the presence of the same MEP modifier found in totally homogeneous systems such as those listed above.
As reported in Coon, the insoluble Cr(III)-exchanged carboxylic acid resin catalyst offered several advantages over comparable homogeneous catalysts. These advantages included lower residue formation, filtration of the insoluble catalyst from the homogeneous product mix, easier recycling of the catalyst in bead form, and the capability of continuous processing. However, the same fundamental problem present in Thomas, et al. and the other art also exists with the catalyst and modifier system reported in Coon. To completely isolate the combined reaction catalyst and modifier from the homogeneous product mix and to then go forward to recover the .alpha.-tetralone product, a multi-step separation process must take place still involving difficult and costly distillation procedures to remove the homogeneous MEP modifier.
Moreover, additional problems are evident with the catalyst disclosed in Coon. It is known that the Dowex.RTM. CCR-2 carboxylic acid resin, for example, can be damaged by prolonged contact with strong oxidizing agents, and that its maximum suggested operating temperature is only 120.degree. C. These are both significant limitations effectively reducing its commercial utility.
The applicants' novel insoluble catalyst compositions and processes for utilizing the same, as disclosed herein, solve these fundamental problems found in prior art whole-or part-homogeneous catalyst systems both in Tetralin.RTM. or other oxidation reactions. The applicants' catalysts provide considerable advantages over the two-part catalyst and modifier combinations such as disclosed in Thomas et al. and Coon. In the applicants' catalysts, pyridine ligands to improve reaction selectivity and an effective chromium salt are both directly bound to and supported by a single insoluble polymer structure, thereby creating a one-part totally insoluble catalyst system. The need for a separate homogeneous modifier, such as the MEP used in Thomas et al. and Coon, and the attendant additional processing and recovery steps are therefore eliminated.
With applicants' catalysts, there is instead simply a single standard filtration or similar separation step required, such as decantation or the like, to remove the insoluble supported catalyst from the otherwise homogeneous product mix. Ease of separation and recovery and lower processing costs, along with greater recycling efficiencies, are thus realized over prior art catalyst systems. The applicants' preferred insoluble supported catalysts are also strongly resistant to oxidation degradation and demonstrate a far broader range of operable temperatures to at least about 225.degree. C., which are significant factors demonstrating their commercial practicality. Additional unexpected benefits have been lower residue produced in the product mix and, for example, the absence of any side formation of .alpha.-Tetralin.RTM. hydroperoxide in the Tetralin.RTM. oxidation.